This invention relates to a magnetic head for perpendicular magnetic recording and reproduction. Perpendicular magnetic recording enables signals to be recorded with much higher density than the conventional longitudinal magnetic recording. As a head for recording and reproducing such perpendicular magnetic signals, the following heads have been proposed. FIG. 1 shows a first example of such heads, namely, an auxiliary-pole-driven perpendicular magnetic head in which a main pole 1 and an auxiliary pole 3 with a winding 2 oppose each other with a medium 4 therebetween. A second example, namely, a main-pole-driven perpendicular magnetic head which makes improvements on the first example is shown in FIG. 2, and enables recording and reproduction from one side of the medium.
Both of these heads signals are recorded on a medium by applying a recording current to the winding 2, and are reproduced by virtue of a voltage induced in the coil by the magnetized medium, and it is known that the closer the winding is positioned to the medium, the higher the efficiency is.
A head of thin film structure is effective in providing a coil at a position as close as possible to a medium in a main-pole-driven perpendicular magnetic head. FIG. 3 shows a third example having this structure.
The main pole 1 formed of a magnetic thin film, a thin film coil 6 and a return yoke 7 formed of a magnetic thin film are laid on top of one another in this order on a non-magnetic substrate 5. An insulation layer (not shown) is formed between the films. This structure can reduce the entire size of the head, especially the dimension of L.sub.1 shown in FIG. 3, of a thin film head of this structure, and thus can provide a coil with high efficiency. A head which has a coil of approximately 10 turns of winding and in which the dimension L.sub.1 is approximately 100 .mu.m has been realized with this structure.
Furthermore, a fourth example has been proposed in which the winding is brought even closer to the medium, as is shown in FIG. 4.
The thin film coil 6 is formed on a magnetic substrate 8, to which the main pole 1 held by a non-magnetic substrate 9 is bonded. This structure makes the distance between the coil and the medium L.sub.2 shorter than L.sub.1, and makes it possible to obtain a head with higher efficiency.
The above-described perpendicular heads which have hitherto been proposed will now be compared in the following.
In the first and second examples, a coil can have several tens to several hundred of turns, but since the diameter of the wire is several tens .mu.m, the entire dimension of the coil becomes more than several hundreds of .mu.m, this makes the miniaturization of a coil unattainable, thus placing a limit upon the efficiency of the head.
In the third and fourth examples which use a coil of several .mu.m both in width and thickness, it is possible to realize a highly efficient head with a coil of small dimension and hence the head itself can be kept small.
It is contemplated to realize a large number of turns as in the first and second examples while employing a thin-film structure as in the third and fourth examples.
FIGS. 5a and 5b show the flows of the magnetic flux of the heads shown in FIGS. 3 and 4, respectively. The magnetic flux flows in the manner indicated by the arrows and it is found that there are magnetic lines of force which leak without interlinking the entire coil. It is necessary to enlarge the dimensions A in FIG. 5a and B in FIG. 5b in order to increase the number of turns of the thin film coils. However, the more distant the coil becomes from the main pole, the lower becomes the number of flux interlinkage. Accordingly, the realization of a coil constructed in the manner as described above and having several tens to several hundred turns will not go far toward heightening of the absolute output. On the other hand, if a multi-layer thin film coil (e.g. 10 turns.times.10 layers) is realized, the head will be highly efficient, but this may prove impractical since the manufacturing process becomes considerably complicated to be impractical.
To sum up, according to the first and second examples a head of low efficiency with a large number of coil turns and according to the third and fourth examples a head of high efficiency but with a small number of coil turns, respectively, are the only forms realizable, and with respect to head output, which is the most important factor from the practical point of view, none of them are satisfactory.